This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPP third generation partnership project
ARFCN absolute radio frequency channel number
BCH broadcast channel
BW bandwidth
CC component carrier
CN core network
DL downlink (eNB towards UE)
eNB EUTRAN Node B (evolved Node B)
EPC evolved packet core
EUTRAN evolved UTRAN (LTE)
HSPA high speed packet access
IMSI international mobile subscriber identifier
LTE long term evolution
LTE-A long term evolution advanced
MAC medium access control
MIB master information block
MM/MME mobility management/mobility management entity
Node B base station
OFDMA orthogonal frequency division multiple access
O&M operations and maintenance
PDCP packet data convergence protocol
PDSCH physical downlink shared channel
PHY physical (Layer 1)
RACH random access channel
RAN radio access network
RLC radio link control
RRC radio resource control
SC-FDMA single carrier, frequency division multiple access
SCH shared channel
SGW serving gateway
SIB system information block
SIM subscriber identity module
UE user equipment
UL uplink (UE towards eNB)
USIM universal subscriber identity module
UTRAN universal terrestrial radio access network
The specification of a communication system known as evolved UTRAN (EUTRAN, also referred to as UTRAN-LTE or as EUTRA) has been discussed within the 3GPP. As specified the DL access technique is OFDMA, and the UL access technique is SC-FDMA.
One specification of interest is 3GPP TS 36.300, V8.7.0 (2008-12), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (EUTRA) and Evolved Universal Terrestrial Access Network (EUTRAN); Overall description; Stage 2 (Release 8). This system may be referred to for convenience as LTE Rel-8, or simply as Rel-8. In general, the set of specifications given generally as 3GPP TS 36.xyz (e.g., 36.211, 36.311, 36.312, etc.) may be seen as describing the Release 8 LTE system. More recently, Release 9 versions of at least some of these specifications have been published.
FIG. 1A reproduces FIG. 4.1 of 3GPP TS 36.300, and shows the overall architecture of the E-UTRAN system. The E-UTRAN system includes eNBs, providing the EUTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE. The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an S1 interface to an EPC, more specifically to a MME (Mobility Management Entity) by means of a S1 MME interface and to a Serving Gateway (SGW) by means of a S1 interface. The S1 interface supports a many to many relationship between MMEs/Serving Gateways and eNBs.
The eNB hosts the following functions:
functions for Radio Resource Management: Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both uplink and downlink (scheduling);
IP header compression and encryption of the user data stream;
selection of a MME at UE attachment;
routing of User Plane data towards Serving Gateway;
scheduling and transmission of paging messages (originated from the MME);
scheduling and transmission of broadcast information (originated from the MME or O&M); and
measurement and measurement reporting configurations to provide mobility and scheduling.
Of particular interest herein are the further releases of 3GPP LTE targeted towards IMT-A systems, referred to herein for convenience simply as LTE-Advanced (LTE-A).
Reference can be made to 3GPP TR 36.814, V1.2.1 (2009-06), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Further Advancements for E-UTRA Physical Layer Aspects (Release 9). Reference can also be made to 3GPP TR 36.913, V8.0.1 (2009-03), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Requirements for Further Advancements for E-UTRA (LTE-Advanced) (Release 8). A goal of LTE-A is to provide significantly enhanced services by means of higher data rates and lower latency with reduced cost.
As specified in 3GPP TR 36.913, LTE-A should operate in spectrum allocations of different sizes, including wider spectrum allocations than those of Rel-8 LTE, e.g., up to 100 MHz, to achieve the peak data rate of 100 Mbit/s for high mobility and 1 Gbit/s for low mobility. It has been agreed that carrier aggregation is considered for LTE-A in order to support bandwidths larger than 20 MHz. Carrier aggregation, where two or more component carriers (CC) are aggregated, is considered for LTE-A in order to support transmission bandwidths larger than 20 MHz. The carrier aggregation could be contiguous or non-contiguous.
A terminal may simultaneously receive one or multiple component carriers depending on its capabilities. An LTE-A terminal with reception capability beyond 20 MHz can simultaneously receive transmissions on multiple component carriers. An LTE Rel-8 terminal can receive transmissions on a single component carrier only, provided that the structure of the component carrier follows the Rel-8 specifications.
FIG. 1B shows an example of the carrier aggregation, where M Rel-8 component carriers are combined together to form MxRel-8 BW, e.g. 5×20 MHz=100 MHz given M=5. Rel-8 terminals receive/transmit on one component carrier, whereas LTE-A terminals may receive/transmit on multiple component carriers simultaneously to achieve higher bandwidths.
Moreover, it is required that LTE-A should be backwards compatible with Rel-8 LTE in the sense that a Rel-8 LTE terminal should be operable in the LTE-A system, and that a LTE-A terminal should be operable in a Rel-8 LTE system.
Of interest herein is E-UTRAN LTE-A idle mode mobility and load balancing. The carrier where a given UE is camping in the IDLE mode is unknown to the eNB. While the eNB has certain means to control the UEs as to which carrier they camp on, the control information is typically the same for all UEs and is not cell-specific. A particular UE changing from the IDLE state to the ACTIVE state consumes RACH resources in that cell. The UE becomes RRC-connected and, without being explicitly signaled, stays RRC-connected in that cell.
With further regard to carrier aggregation, what is implied is that one eNB can effectively contain more than one cell on more than one CC (component carrier), and the eNB can utilize one (as in E-UTRAN Rel-8) or more cells (in an aggregated manner) when assigning resources and scheduling the UE.
A Rel-8 UE will camp on a cell on a carrier frequency according to the absolute priority set for the frequencies. That is, the Rel-8 UE will attempt to camp on a cell of the highest priority frequency. Priorities used for the camping purpose are normally broadcast by the network, but the eNB can also signal dedicated priorities for the UE when the UE moves from the RRC_Connected to the RRC_Idle states, and these priorities remain in effect for some fixed duration (T320 timer, whose maximum length is 3 hours.) Using the broadcast technique for distributing frequency priority information implies that the UEs would all tend to camp on the same CC of the eNB. This can result in unbalanced UL load, for example, due to Random Access procedures.
Rel-8 assumes absolute priorities for frequency layers. With these, the UE attempts to stay on a highest priority layer as long as possible, while taking the radio conditions in the frequency layer into account. The UE uses certain thresholds (given by the network) into account (depending on radio conditions) when deciding whether to reselect to another carrier frequency. If the eNB signal level in the current frequency is worse than a given threshold, the UE is allowed to reselect to another frequency if an eNB signal level on that frequency is better than (another) given threshold.
The exact behavior and potential thresholds and parameters are described in more detail in 3GPP TS 36.304 V9.0.0 (2009-09) Technical Specification 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) procedures in idle mode (Release 9), and in 3GPP TS 36.331 V9.0.0 (2009-09) Technical Specification 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) Radio Resource Control (RRC); Protocol specification (Release 9).
Reference may also be made to R2-094545, 3GPP TSG-RAN-WG2 Meeting #66bis, Shenzhen, P. R. China, Aug. 24-28, 2009, “Carrier Aggregation-Paging Optimization”, Motorola. In R2-094545 it is stated that in this option, both the UE and the network use a hashing function to determine an ordered list of preferred camping carriers, based on the UE-id (IMSI, for example). The UE always camps on the most preferred carrier, provided that the carrier is capable of camping and there is coverage of that carrier at the current location of the UE. Because the network also knows this hash function, it can determine the most likely carrier in which the UE is camping. An appropriate paging algorithm can then be designed to use this ordering to preferentially page the UE in one or more carriers of the UE as per the preferred list. The hashing function can be designed in a fashion that the UEs are distributed across the different component carriers to distribute the paging load evenly.